1. Field of the Invention
The present invention generally relates to label multiplexing type switching networks, such as an ATM (Asynchronous Transfer Mode) switching network and a frame relay switching network. More specifically, the present invention is concerned with a switching node capable of forming integrated communications systems in the label multiplexing type switching networks.
2. Description of the Related Art
Recently, there has been considerable activity in the development of label multiplexing type switching networks capable of equally handling a variety of data, such as audio data, dynamic image data and high-speed data. Examples of these label multiplexing type networks are ATM switching networks and frame relay switching networks. In these switching networks, label type (packet type) data is multiplexed with information to be transferred through a user-network interface (UNI) or a network-node interface (NNI). An identifier for communication identification is added to a header of each packet. As is well known, the user-network interface couples terminal equipment (TE) and switching nodes with each other, and the network-node interface couples the switching nodes with each other.
FIG. 1 shows a conventional label multiplexing type network. In order to efficiently transfer information, a plurality of virtual channels (VC; also called virtual circuits) are defined on a single physical line (UNI or NNI). In this manner, multiplexed transmission is realized.
A predetermined virtual channel VC (which is depicted by a thick solid line in FIG. 1) is a permanent virtual channel (PVC) for signaling. The permanent virtual channel is also called a permanent virtual circuit. In the network, in advance of actual call communications, call control information is exchanged between the terminal equipment and the switching nodes or between the switching nodes, using the signaling channel. A call control processor in each switching node executes a call control process based on the call control information. By this call control process, a logical communications path having a fixed route is established between the terminals TE, and hence messages can be transferred between them. Thereafter, a label exchange switch in each of the switching nodes makes a connection between the virtual channels on the UNI or NNI. In this state, terminal-to-terminal communications can be performed. After the end of the communications, the call control processor in each of the switching nodes releases the logical communications path being used.
Communications services having a call control process as described above are called connection-oriented type (CO type) communications services, and a basic communications protocol in the label multiplexing type network, such as ATM networks and frame relay networks.
In integrated services networks as described above, there is an increasing demand for communications services other than normal communications services. In such additional or secondary communications services, it is required that information be transferred at high speed (or in real time) in a single message format. Examples of these secondary communications services are telemetering that gathers information from remote terminals, a computer network system connected between local area networks, and a transaction process in which an updating process of a database is executed, such as a seat reservation system or a banking system.
If the above-mentioned secondary communications services are provided by means of the label multiplexing type switching network, the following first and second method would be possible. The first method is such that the secondary communications services are provided as the connection-oriented type communications services. That is, call setup and call releasing processes are carried out for each single message which generates the communications request. The second method is to provide a permanent virtual channel PVC for each terminal TE which may utilize single-message communications. Each single-message is transferred through the above permanent virtual channel PVC.
However, the first and second methods have the following respective disadvantages. It is required that the call connection process should be performed at high speed in view of the performance of the communications services for telemetering and the transaction process. However, the first method must execute the call setup process and the call releasing process for each single-message. These processes are a large load of the call control process, and considerably degrades the ability of the call control process.
The second method does not need to execute the call setup process and the call releasing process for each single-message. However, the permanent virtual channel PVC is always occupied by the specific terminal equipment, and the resources of the network (channel resources) cannot be efficiently utilized.
A description will now be given of the disadvantages of the switching networks themselves based on the connection-oriented communications services, separately from the above-mentioned disadvantages encountered when the secondary communications services, such as the telemetering process and the transaction process, are provided by the label multiplexing networks.
In the general switching networks capable of providing the connection-oriented communications services, the call control process is carried out in such a manner that when a correction-oriented call is accepted, the terminal equipment is given a maximum band available at this time in order to ensure the quality of communications even if heavy traffic comes from the terminal equipment. However, as shown by hatched areas in (a) of FIG. 2, a large idle band will occur for each virtual call VC. Hence, the band cannot be efficiently utilized.
On the other hand, in the recently developed label multiplexing type switching networks based on the connection-oriented communications services, the information transfer route is fixed during communications. Thus, it is easy to identify the traffic performance of each virtual call in communications and hence to realize quantitative traffic control of the whole network. In addition, communication information can be placed in an idle time slot per cell (frame or packet), and hence any idle time in traffic in each of the virtual calls VC in each link (interface) can be efficiently used. Hence, it becomes possible to realize statistically efficient multiplexing of a plurality of virtual calls.
However, in general, the above statistically effective multiplexing will be expected only when calls having similar traffic characteristics are multiplexed in a large number of channels. Particularly, if traffic having a characteristic similar to that of a burst occurs, other traffic will greatly be affected. As a result, a large delay in transmission of information takes place, and the cell loss probability will increase. With the above in mind, the label multiplexing network is forced to handle a regulated number of virtual calls. Hence, as shown in (b) of FIG. 2, an idle band depicted by a hatched area will be generated in each link (interface), and the resources of the network cannot be efficiently utilized.
As described above, the conventional label multiplexing networks providing the connection-oriented communications services cannot effectively provide the secondary communications services, such as the telemetering and the transaction processing. On the other hand, the resources of the network cannot be effectively utilized if the label multiplexing type networks are designed to provide only the connection-oriented communications services.